The invention relates to a magnetron sputter cathode with a closure element, which can be set into an opening of the housing wall of a vacuum chamber, whereby the opening is closed airtight and the closure element is electrically insulated against the housing wall, with a sputter target on the vacuum side of the closure element, with a magnet configuration on its atmospheric side, and with a cooling plate operated with a cooling fluid for the sputter target and with the further characteristics of claim 1.
A cathode with the characteristics explicitly listed above is described inter alia in U.S. Pat. No. 5,458,759.
In the implementation described in this document the closure element consists of the backing plate of the sputter target provided with a frame, which makes it possible to set the backing plate airtight into an opening of the housing wall of the vacuum chamber, such that the sputter target connected with the backing plate is located in the vacuum chamber. On the atmospheric side of the backing plate there is a cooling plate with open channels which are closed off by the backing plate. Behind it is located a movable magnet configuration whose magnetic field extends to the region in front of the sputter target.
Electrons emitted from the cathode are accelerated by a high voltage applied to the cathode and ionize the gas molecules of a working gas in the vacuum chamber. The positively charged ions generated therein impinge on the sputter target and knock out molecules and atoms, which are deposited in thin layers onto a substrate. The electrons are concentrated in front of the sputter target by the magnetic field such that the ion yield is increased. According to the magnetic field geometry, so-called race tracks form in the sputter target. In order to ensure uniform erosion of the material, the magnet configuration can be shifted.
The arrangement described in U.S. Pat. No. 5,458,759 is only suitable for small sputter targets which have a short useful life. To extend the useful life, widening the sputter target could be considered or disposing several targets adjacent to one another on the closure element. However, the following must be taken into account: the backing plate serving as closure element is exposed to the differential pressure between vacuum and atmosphere and therefore would be deflected at too large a lateral extent. As a consequence, this, in turn, would result in the sputter target, comprising a brittle material, separating from the backing plate or forming cracks. The channels of the cooling plate conducting the cooling water could also no longer be sealed tightly enough by the backing plate. The durability of such an enlarged cathode is therefore not very great. While it would be conceivable to implement the backing plate to be thicker and therewith more stable, this would, however, result in a reduced cooling effect for the sputter target. In addition, the problem would be created that, due to the greater distance from the magnet configuration, the magnetic field in front of the target would be weaker and consequently the ion yield lower.
Therewith the problem needs to be solved of providing a magnetron sputter cathode which, compared to previously known solutions, has a markedly increased useful life.
According to U.S. Pat. No. 6,494,999 B1 the cooling plate is disposed on the vacuum side between the closure element implemented as a carrier and the sputter target.
This realization has the advantage that the cooling plate is located within the vacuum and therewith is closer to the target, whereby the cooling efficiency is improved. The carrier itself is a separate structural element, which can be realized such that it can absorb and brace against the acting pressures without experiencing significant deflection. Since the cooling means in this implementation is located within the vacuum chamber, the carrier requires lead-throughs for the cooling fluid.
Such a disposition permits a significantly wider implementation of the cathode, since the carrier is no longer formed by the backing plate, but rather forms a separate structural element, which can be laid out according to the obtaining pressure loading.
The carrier according to U.S. Pat. No. 6,494,999 B1 includes through-conduits for the cooling fluid.
Since the cooling plate is thus not loaded by differential pressure, the cooling plate can be provided with cooling channels and can simultaneously form the backing plate of the sputter target. The cooling channels within the cooling plate have a closed cross section, such that the one side of the backing plate forms a continuous contact face toward the sputter target. This simplifies establishing the bond between the sputter target and the backing plate implemented as cooling plate.
In order for the requirements made of the resistance to deformation of the carrier under pressure loading not to be too high, it is proposed that spacers are provided between the backing plate and the carrier, such that a gap remains between the central region of the backing plate and the carrier.
The problem addressed by the invention, consequently, comprises providing a secure seating for a backing plate to be implemented as thin as possible.
According to the invention the spacers are formed by webs (13), on which the margin of the backing plate (3) is fastened in contact, with its side facing away from the sputter target, such that when the vacuum chamber is evacuated, the gap is also evacuated, and that the gap permits the deflection of the carrier, since the backing plate, and therewith the sputter target, are free of pressure differential.
If during the fastening of the backing plate on the carrier plate a lateral tolerance at the webs is specified, the backing plate is not forced to follow a deflection of the carrier along. The backing plate remains straight and there is no risk of the sputter target detaching from the backing plate.
In the simplest case the spacers are formed integrally with the carrier, the conduction of the cooling fluid taking place through the webs.
This also permits, inter alia, the supply to the channels in the backing plate to take place via the fastening of the backing plate on the webs.
In order for the carrier itself not to become too thick, whereby the magnets would have to be disposed at too great a distance from the sputter target, it is furthermore proposed that the carrier on the atmospheric side has at least on its longitudinal sides two marginal reinforcement ribs. These can simultaneously serve for the purpose of fitting the carrier into the opening. It is understood, that an encompassing reinforcement rib could also be provided such that the carrier assumes a tub-form shape.
In the case in which the cathode is implemented to be wider, it can additionally be provided that not a unitary sputter target is provided, but rather that on the carrier are disposed at least two elongated sputter targets adjacent to one another, each with a backing plate, with one magnet configuration generating a race track being assigned to each sputter target.
The disposition of several sputter targets also has the advantage that the individual sputter targets do not become excessively heavy and consequently remain manageable.
However, individual elongated sputter targets could also become very heavy. It is therefore proposed that each sputter target is composed of several sputter target segments abutting one another. Moreover, to each sputter target segment its own backing plate is assigned, which, for this purpose, is also segmented. Each individual segment comprises its own cooling water circulation with its own cooling water supply. In principle, segmentation can also be carried out if the backing plate is the closure element itself.
Such a configuration has also the advantage that the cooling circulations do not become too long, such that even at the end of the circulation the cooling water is still sufficiently cool and has adequate cooling capacity, such that the target has a uniform temperature overall.
For clarification, the invention will be explained in the following in further detail in conjunction with an embodiment example. In the drawing depict: